Ulster saw out the final 10 minutes with 13 men to inflict a four-try defeat on a beleaguered Dragons side.
Luca Sperandio and Niccolo Cannone scored two tries apiece as Benetton Treviso stretched their unbeaten run to eight games.
Centre Stuart McCloskey celebrated a century of matches for Ulster by dotting down for the only try against the Ospreys.
Southern Kings produced a stunning late fightback to claim only their second win of the season, halting Edinburgh's impressive run.
Northampton scored 17 tries in a record victory as they beat Timisoara Saracens 111-3 to reach the European Challenge Cup quarter-finals.
Former Wales prop Ceri Jones will keep hold of the reins at Pro14 side the Dragons for the remainder of the season.
Jason Tovey's late penalty gave the Dragons a first win over the Ospreys since Boxing Day 2014.
The Dragons looked set to earn a draw despite playing for almost 50 minutes with a man down, but Cardiff Blues denied them right...
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The Dragons have parted ways with head coach Bernard Jackman, who was appointed to the role at the Pro14 club in June 2017.
Jared Rosser scored two tries as the Dragons claimed a much-needed victory in Sunday's Pro14 action.
There were wins for Connacht and Ulster in Saturday's Pro14 action.
Zebre stunned Edinburgh, Scarlets denied Southern Kings and there was landmark win for Ulster in Pro14 on Friday.
Having been beaten 82-21 by La Rochelle six days earlier, Enisei were once again outplayed by the French club.
Worcester Warriors had lost 11 away games in a row in the Challenge Cup, but ended that sequence with a brilliant showing in Paris.
Leinster are five points clear at the top of Conference B after the defending champions beat Munster at the Aviva Stadium.
The Southern Kings claimed a first Pro14 win of the season and consigned Glasgow Warriors to a first loss in Port Elizabeth.